The oxygen isotope ratios of diatom (δ18Odiatom) and the oxygen and hydrogen isotope ratios of lake water (δW) of lakes in south Alaska provide insight into past changes in atmospheric circulation. Lake water was collected from 31 lakes along an elevational transect and diatoms were isolated from lake sediment from one lake (Mica Lake) in south Alaska. In general, δW values from coastal lakes overlap the global meteoric water line. δW values from interior lakes exhibit lower values, however, indicating that they are influenced by evaporation. Sediment cores were recovered from 58 m depth in Mica Lake (60.96° N, 148.15° W; 100 m above sea level), an evaporative-insensitive lake in the western Prince William Sound. Thirteen calibrated 14C ages on terrestrial macrofossil samples were used to construct an age-depth model for core MC-2, which spans 9910 yr. Diatoms from 46, 0.5-cm-thick samples were isolated and analyzed for their oxygen isotope ratios. The analyses employed a newly designed, stepwise fluorination technique, which uses a CO2 laser-ablation system, coupled to a mass spectrometer, and has an external reproducibility of ± 0.2‰. δ18Odiatom values from Mica Lake sediment range between 25.2 and 29.8‰. δ18Odiatom values are relatively uniform between 9.6 and 2.6 ka, but exhibit a four-fold increase in variability since 2.6 ka. The 20th century shows a 4.0‰ increase of δ18Odiatom values. Shifts of δ18Odiatom values are likely not related to changes in diatom genera assemblage or dissolution effects. Late Holocene excursions to lower δ18Odiatom values suggest a reduction of south-to-north storm trajectories delivered by meridional flow, which likely corresponds to prolonged intervals when the Aleutian Low pressure system weakened. Comparisons with stable isotope of precipitation (δP) records from the region support the storm-track hypothesis, and add to evidence for variability in North Pacific atmospheric circulation during the Holocene.